The present invention relates to an electrophotographic photoreceptor of a function separation type for long wavelength light which comprises an Ashd 2SE.sub.3 carrier transport layer, a 30 to 50 wt% Te-Se alloy carrier generation layer and an As .sub.2 SE.sub.3 surface protective layer.
In the printer of an electrophotographic system, light of long wavelength, such as 630 to 800 nm, is used as writing light for forming an electrostatic latent image on the surface of a photoreceptor. In such a printer, a function separation type photoreceptor composed of a carrier generation layer that has a high sensitivity even to long wavelength light, a carrier transport layer for transporting the carrier produced on the carrier generation layer, and a surface protective layer for protecting the carrier generation layer from external stress are generally used. In such a photoreceptor, a high-concentration Te-Se alloy is generally used for the carrier generation layer, amorphous Se material is generally used for the carrier transport layer and a low-concentration As-Se alloy is generally used for the surface protective layer. The surface protective layer is an important layer that determines the life of a photoreceptor. However, a low concentration As-Se alloy, which has a high thermal expansion coefficient as compared with As.sub.2 SE.sub.3 and a low mechanical strength, is generally used in order to avoid cracking due to differences in the thermal expansion coefficients of the surface protective layer and the carrier transport layer, which generally comprise amorphous Se material having a very large thermal expansion coefficient.
Such a photoreceptor disadvantageously has an insufficient printing durability. In an effort to enhance the mechanical strength of the surface protective layer by simultaneously lowering the thermal expansion coefficients of the carrier transport layer and the surface protective layer, an Se-Te-As function separation type photoreceptor for a laser beam printer having a high printing durability has recently been developed.
Such an Se-Te-As photoreceptor realizes a high printing durability on the same level as a conventional As.sub.2 SE.sub.3 photoreceptor, since the outermost surface layer consists of an As alloy. On the other hand, this photoreceptor also has the same disadvantage of an As.sub.2 SE.sub.3 photoreceptor, namely when exterior mechanical stress or chemical action are applied, the printing quality deteriorates. For example, image defects are produced.
Accordingly, it is an object of the present invention to eliminate the above-described defects in the prior art and to provide an electrophotographic photoreceptor having a high-printing durability, excellent mechanical strength and chemical stability, thereby reducing the possibility of producing image defects even if mechanical stress or chemical action are applied to the surface of the photoreceptor.